Process and apparatus for driving tunnels in rock having zones differing in stability



PROCESS AND APPARATUS FOR DRIVING TUNNELS IN g. 1970 ELAUBER 3,523,426

ROCJK HAVING ZONES DIFFERING IN STABILITY Filed March 25. 1968 5Sheets-Sheet 1 INVENTOR. E R HSTF LA LLB ER AGENT- Aug. 11, 1970 E.LAUBER 3,523,426

PROCESS AND APPARATUS FOR DRIVING TUNNELS IN ROCK HAVING ZONES DIFFERINGvIN STABILITY Filed March 25. 1968 5 Sheets-Sheet 2 r V INVENTOR E R MSTLA WE; e K

Aug. 11, 1970 E. LAUBER 3,523,425

PROCESS AND APPARATUS FOR DRIVING TUNNELS IN ROCK HAVING ZONES DIFFERINGIN STABILITY Filed March 25. 1968 5 Sheets-Sheet 5 F/GJO 1 l 1- FIG]! I1 10 20 901 7 14 121519 19 21 FI 5 9a 7 9 19 1a 1517 20 2 1 INVENTOR.EIQMST LWBQQ Aug. 11, 1970 E. LAUBER 3,523,426

PROCESS AND APPARATUS FOR DRIVING TUNNELS IN ROCK HAVING ZONES DIFFERINGIN STABILITY Filed March 25, 1968 5 Sheets-Sheet 4 FIG. 77

F /G. 79 F/G.76

. INVENTOR. 61m Lm/csefi 3,523,426 LS IN E. LAUB PARA'IUS FOE FROG ANDAP DRIVING TUNNE R0 HAVING ZONES DIFFERING IN STABILITY Filed March 25,1968 5 Sheets-Sheet 5 INVENTOR. ERMgT: LALGBQQ BY m- M United StatesPatent Int. Cl. E61 3/03 US. Cl. 61-85 11 Claims ABSTRACT OF THEDISCLOSURE Zones of stable rock are excavated by a tunnel-drivingmachine having unshielded rotatable and radially adjustable cuttingtools. The tunnel-driving machine is advanced in steps in a zone ofstable rock to the transition to a zone of rock of low cohesion and isoperated during such steps to excavate on a diameter which is largerthan the diameter of the excavation in the preceding portion of the zoneof stable rock. The tunnel driving machine is retracted after each ofsaid advancing steps with the cutting tools in a radially inwardlyadjusted position. A section of a tubular shield is installed ahead ofthe tunnel-driving machine after each of said retracting steps andbefore the next succeeding advancing step. Each section consists of aplurality of separable segments. The tunnel-driving machine is thenanchored in the shield and the latter is advanced through the zone ofrock of low cohesion until stable rock is reached. The tunnel behind theshield is lined with lining rings. The tunnel-driving machine isreleased from the shield when the stable rock is reached and is usedalone for excavating the stable rock. The shield is knocked down.

In the construction of tunnels in loose rock or in strata having only alow cohesion, it is known to use tubular shields having an annularcutting edge at their leading end. Under the protection of the shield,the excavation is carried out manually. It is also known to provide anexcavating device within the shield. The shield is always moved ahead bymeans of hydraulic jacks, which act by means of thrust-bearing ring onthe tunnel lining which is arranged behind the shield. This method ofexcavation is not applicable to relatively hard rock or Where hard rocksoccur in soft material.

Other tunnel-driving machines have been disclosed, which are providedwith rotating cutting tools that may be radially adjustable so that theentire cross-section of the tunnel can be excavated even in moderatelyor very hard rock. Particularly satisfactory service has been given by atunnel-driving machine which has cutting tools in the form of millingcutters which rotate on their own axes and are mounted at the end faceof a drum, which is rotatable on the axis of the machine. This machinemay be used without a shield if the rock is so stable that it issuflicient to install temporary supports adjacent to the machine orbehind the same. The propelling unit of the machine consists in mostcases of hydraulic jacking means and bears 'with static frictiondirectly on the surface of the tunnel so that it is not required toinstall expensive lining rings. The final lining is formed by pumpingconcrete with the aid of a sliding formwork behind the tunnel-drivingmachine.

The use of machines in the excavation of tunnels has not been fullysuccessful before owing to the geological structure of rock. The rockwhich is encountered along the length of a tunnel, particularly one ofgreat length, varies widely in hardness and strength and the conditionof the rock may also vary. Difiiculties arise when zones 3,523,426Patented Aug. 11, 1970 of hard rock having a high stability areimmediately succeeded by zones of rock which is loose and has only a lowcohesion. Another difficulty is due to the fact that unexpectedconditions are apt to occur even .if a thorough geological investigationas to the rock conditions to be expected has been carried out before theconstruction of a tunnel and has been evaluated to obtain information asto the classes of rock.

If soft and hard rocks are to be expected in alternation in theconstruction of a tunnel, it will be impossible to use tunnel-drivingmachines which are suitable only in soft rock. On the other hand, itwill be impossible to use machines that are suitable both for hard andsoft rocks if strata will or may be encountered which have only a lowcohesion. It might appear obvious to replace the well known excavatingmachines for soft, homogeneous material by a known tunnel-drivingmachine for soft and hard rock and to install such machine permanentlyin a tubular shield. The adoption of this method is impossible in mostcases in view of the high expense which is involved in it because theuse of a shield requires the subsequent installation of lining rings anda complete lining of long tunnels with lining rings is much moreexpensive than, e.g., a lining consisting of concrete placed with theaid of a formwork.

It is an object of the invention to provide an economical process whichenables the use of machine in the driving of tunnels at least under rockconditions which are frequently encountered.

Based on a process for the construction of tunnels or the like in rockhaving zones differing in stability and with the aid of a tunnel-drivingmachine having rotating and radially adjustable cutting tools, whichpreferably consist of milling cutters that are adapted to revolve inunison about the longitudinal axis of the machine, the process accordingto the invention is essentially characterized in that the tunnel isdriven in zones of stable rock in the usual manner with the aid of thetunnel-driving machine alone whereas upon the arrival at a zone of rockhaving a low cohesion a tubular shield consisting of a plurality ofsections which can be knocked down into segments is installed onesection after the other in the zone of stable rock ahead of thetunnel-driving machine while the latter is advanced in steps andoperated to excavate at a diameter which is larger than the previoustunnel diameter, the tunnel-driving machine is subsequently retractedwith the cutting tools in a radially inwardly adjusted position, and isthen firmly anchored in the shield, the latter is advanced, the tools ofthe tunnel driving machine are operated, if desired, during the advanceof the shield, and the tunnel or the like is lined with lining ringsbehind the shield until the next zone of stable rock is reached, whenthe tunnel-driving machine is released from the shield and propelledalong and the shield is knocked down for its next use. When inferiorrock is encountered in the driving of a tunnel or the like and such rockcannot remain in a stable condition until the temporary lining can beinstalled, the shield will be used so that the tunnel-driving machine isdisposed within the protecting shield While the zone of low cohesion isbeing traversed. The occurrence of inferior rock may be detected, e.g.,'by test bores driven ahead of the tunnel. In the zone of inferior rock,the excavation is carried out only with the aid of the shield. In thenormal case, however, the cutting tools of the tunnel-driving machineare in operation ahead of the cutting edge of the shield. Only when therock caves in, e.g., in loose gravel, the tunnel-driving machine isretracted into the shield to such an extent that the cutting tools arebehind the cutting edge of the shield. The tunnel is lined in the usualmanner with lining rings behind the shield. In the normal case, however,the cutting tools of the tunnel-driving machine is released from theshield and moves out of the tubular shield with the aid of thepropelling unit associated with the machine. The expensive lining withlining rings is required only where it is actually essential, namely, inthe zone of rock of low stability, whereas in zones of rock having asufiiciently high stability the tunnel is driven in the usual manner andcan -be lined with concrete placed with the aid of a framework or withother means which are much more economical. It is not necessary tomodify the tunnel-driving machine, which may be used also alone. Theshield which can be knocked down can easily be stored, assembled andtaken apart and can be used as often as desired.

When test bores are driven ahead of the tunnel so that the zone of lowstability is detected early, the excavation of increased diameter can beinitiated at a point which is spaced from the zone where the poor rockis to be expected by a distance which is at least as large as the lengthof the shield. Alternatively, the tunnel may be driven with the aid ofthe tunnel-driving machine alone as far as to the zone of rock of lowcohesion, i.e., until the cutting tools begin to enter that zone,whereafter the tunnel-driving machine is retracted by a distance whichis at least as large as the length of the shield and subsequentlyenlarges the previously driven tunnel or the like by twice the thicknessof the shield segments. The latter mode of operation has the advantagethat the removal of the excavated material is much easier during thecutting on the enlarged tunnel diameter than during the excavation ofthe full cross-section and that segments from which the shield tube willbe assembled can be stored in the free space which is created ahead ofthe tunnel-driving machine.

According to the invention, an annular groove is excavated in the tunnelor the like ahead of the tunnel-driving machine which has been retractedand the cutting tools of the tunnel-driving machine are adjusted to theincreased excavating diameter in said groove so that this adjustment canbe carried out without difficulty.

According to the invention the rearmost two sections of the shield areinstalled first and are knocked down behind the tunnel-driving machinewhen the shield has been completely assembled, Whereafter said twosections are replaced by thin sheet metal elements welded together ininstalled position, a thrust-bearing ring is installed in known mannerinto the resulting shield tail, hydraulic jacks for advancing the shieldare caused to bear against said thrust-bearing ring, and the firstlining ring is installed behind the thrust-bearing ring.

The apparatus for carrying out the process according to the inventioncomprises a tunnel-driving machine having a hydraulic propelling means,and a shield which is adapted to be knocked down into segments and to beadvanced with the aid of hydraulic jacks bearing on a thrustbearingring. The pump or like means for propelling the tunnel-driving machineis adapted to be switched over to supply the hydraulic jacks associatedwith the shield so that there is no need to provide a separate source ofpressure oil for supplying the hydraulic jacks associated with theshield.

If the cutting tools of the tunnel-driving machine are carried by a drumwhich is rotatable on the axis of the machine, it is a further featureof the invention to provide on the end face of the drum a bracketlikedevice for installing the shield segments, which device is provided Withscrews or the like extending radially with respect to the drum axis. Inthat case, the rotation of the drum is utilized to distribute the shieldsegments in assembling the length sections of the shield, and the screwsserve to engage the segments with the tunnel surface.

The end face of the drum may be provided between the cutting tools withcompartments which are forwardly open so as to avoid a caving-in ofsubstantial quantities of loose material during shield tunneling.

To enable an adaptation of the shield to different tunnel diameters,bars which are wedge-shaped in cross-section are provided and areinsertable between those edge faces of the arcuate shield segments whichare parallel to the shield axis. The shield segments themselves arealways the same. The wedge-section bars are added or bars having adifierent wedge-shaped cross-section are used in dependence on thedesired tunnel diameter. When the tunnel diameter increases beyond acertain size, an additional segment may be used instead of the spacingbar or bars, and the resulting section or ring may then be enlarged withthe aid of spacing bars. To enable a guided movement of the heavytunnel-driving machine in the tubular shield, the arcuate shieldsegments have stiffening rings which are parallel to the axis of theshield.

The process according to the invention and the apparatus for carryingout the process will be explained more fully hereinafter with referenceto the accompanying drawings in which FIGS. 1 to 1-8 are diagrammaticviews illustrating the various process steps. In these figures, theparts which are essential for the respective operation are indicated bythicker lines.

FIG. 19 is a diagrammatic end elevation showing the tunnel-drivingmachine.

FIG. 20 is a vertical sectional view taken on line XX XX of FIG. 21 andshows a portion of alength section of the shield.

FIG. 21 is an interior View showing the shield portion.

FIG. 22 is a view similar to FIG. 20 and shows a different spacer barand a different installing device.

According to FIG. 1, test bores 3 are driven ahead of a tunnel 2, whichhas been constructed with the aid of a tunnel-driving machine 1. Withthe aid of these test bores a zone 4 of rock of low cohesion isdetected. The tunneldriving machine 1 provided with radially adjustablemilling cutters 5 is now retracted about two meters from the face of thetunnel. Thereafter, a worker excavates an annular groove 6 in the tunnel2 with the aid of a pneumatic drill. The tunnel-driving machine 1 thenadvances as far as to the annular groove 6, and the milling cutters 5are adjusted radially outwardly for driving a tunnel having an enlargeddiameter, which exceeds the original tunnel diameter by twice thethickness of the shield segments which are to be installed.

If test bores 3 are not drilled during the driving of the tunnel, themilling cutters 5 of the tunnel-driving machine 1 will cut directly intothe zone 4 of rock of low cohesion, as is indicated in dotted lines inFIGS. 1 to 7. When this occurs, the tunnel-driving machine 1 must moveback to the position shown in FIG. 1 before the excavation on theincreased diameter can begin so that the tubular shield can subsequentlybe installed in stable rock.

When the milling cutters 5 have been adjusted radially outwardly, thetunnel-driving machine 1 advances by about 1 meter. During this advance,the machine cuts only to increase the tunnel diameter or throughout thecrosssection. In this phase, the tunnel-driving machine is guided in thetunnel 2 by means of a lower skid 7 and a top protecting roof 8. Whenthe desired length of tunnel has been driven (FIG. 2), the millingcutters 5 are adjusted to the initial diameter or to a retractingdiameter and the tunneldriving machine 1 is retracted about 2 meters. Aworker shovels the residual loose material to the conveyor of thetunnel-driving machine (FIG. 3).

The conveyor of the tunnel-driving machine 1 is then reversed and may beused to move shield segments 9 ahead of the tunnel-driving machine 1. Todistribute the shield segments 9, a bracketlike installing device 11 issecured to the end face of the drum 10 of the tunnel-driving machine,which drum carries the milling cutters 5. With the aid of the drumdrive, the shield segments 9 are subsequently swung into the correctposition, moved with the aid of radially extending spindles to thetunnel surface and bolted together (FIG. 4). When all shield segmentshave been bolted together to form a section of the shield,

the installing device 11 is removed and the tunnel-driving machine 1advances to the face of the tunnel or to the position assumed at the endof the preceding cycle of operations. Thereafter the milling cutters 5are adjusted radially outwardly and the tunnel is driven for anadditional length of about 1 meter (FIG. 5). When this length of tunnelhas been driven, the milling cutters 5 are moved back to the retractingdiameter, the machine is retracted and a worker cleans the milled tunnelsection for the installation of the next section of the shield. This isshown in FIG. 6. The installing device 11 is then secured once more tothe drum 10. The conveyor of the tunnel-driving machine is operated inthe forward direction to supply new shield segments, which are assembledto form the next section of the shield with the aid of the installingdevice. FIG. 7 shows the installation of the final segment at the roofof the tunnel.

The operations shown in FIGS. 4 to 7 are repeated several times untilthe position shown in FIG. 8 has been reached. Thereafter thetunnel-driving machine advances for the installation of the last sectionof the shield. During this operation, the propelling unit 12 of thetunneldriving machine 1 bears on the inside of the assembled tubularshield under the action of the pressure applied to strutting jacks 13whereas propelling jacks 14 force the machine against the face of thetunnel.

FIG. 9 shows the insertion of the last section of the shield when thetunnel-driving machine 1 has been retracted a suitable distance. Thesegments 9a form a wedge-shaped annular cutting edge at the free end ofthe shield in order to facilitate the subsequent penetration of theshield into the rock or loose material.

When the segments 9a have been bolted together, the propelling unit 12,13, 14 advances the machine 1 to the face of the tunnel. The millingcutters 5 are then adjusted to the increased diameter and the entirepropelling unit is fixed in the tubular shield with the aid of wedges15. The wedges 15 must subsequently transmit the propelling pressurefrom the shield to the tunnel-driving machine 1. The trailing sectionsof the shield, which were installed first, are then knocked down andremoved. This operation and the following assembling work may be carriedoutwith the aid of the machine for placing the lining rings. Thetrailing sections of the shield are replaced by thinwalled sheet metalelements, which are assembled to the correct diameter in the tunnel andwelded together. A thrust-bearing ring 17 is installed in the resultingshield tail 16. Hydraulic jacks 18 bear on the thrust-bearing ring 17 aswell as on abutments 19 which are secured to the shield (FIG.

FIG. 11 shows the beginning of the lining of the tunnel with the usuallining ring segments 20. The jacks 18 are retracted to pull thethrust-bearing ring 17 to the shield. The lining ring segments areinserted into the space which has thus been cleared in the shield tail16 and are bolted together. The lining ring segments shown in thedrawing consist of pressed steel plates. Alternatively, concrete liningring segments 20a shown in FIG. may be employed. Concrete lining ringsare heavier, however, and their larger thickness inhibits the retractionof the tunnel-driving machine 1. Back-filling concrete 21 is placed fortransmitting the reaction forces due to the propulsion of the shieldfrom the lining ring segments to the tunnel wall 2. To advance theshield, the jacks 18 are extended by the width of a lining ring (FIG.l2). During this operation, the jacks 18 bear through the thrust-bearingring 17, the lining ring segments 20 and the baclofilling concrete 21 onthe tunnel wall 2. By this operation, the tubular shield and thetunnel-driving machine 1 secured in it are advanced. The pump or thelike of the propelling unit 12, 13, 14 is switched over to supplypressure oil to the jacks 18. The latter are then retracted so that thethrust-bearing ring 17 follows and the segments 20 for the second liningring can be installed (FIG. 13). FIG. 14 shows another step of advancingthe shield when the second lining ring has been assembled.

To enable a driving of the tunnel in a prescribed direction or with adesired curvature, provision must be made for lateral and heightcorrections during the driving of the tunnel. For such corrections, theaxis of the tunneldriving machine 1 is displaced or pivotally movedrelative to the axis of the shield. Thereafter, only the milling cuttersare cutting in the new direction and the shield follows owing to thereduced resistance in that area. The machine may also be advanced andretracted in the shield for making corrections.

In the position shown in FIG. 17, the tunnel has been driven in theloose zone to such an extent that the rear part of the tunnel-drivingmachine slides on the lining ring segments 20. That rear part consistsof a platform 22 resting on skids. The body of the tunnel-drivingmachine is provided at its rear end with a pin 23, which is held in asteering device 24 for vertical and horizontal adjustment. This steeringdevice may be used to effect the desired correcting adjustment of theaxis of the tunneldriving machine relative to the axis of the shield.

When the zone of low cohesion has been traversed and stable rock hasbeen reached, the jacks 18, the thrustbearing ring 17 and the abutments19 are removed. To compensate for the difference in height, two fillingrings 25 are installed in the shield tail 16 and the milling cutters areadjusted back to the normal tunnel diameter. The wedges 15 are removedto release the tunnel-driving machine and the source of pressure oil isconnected to the propelling unit of the tunnel-driving machine. When thetunnel-driving machine 1 moves out of the shield (FIG. 17), thepropelling unit bears temporarily on the shield segments 9, and theskids of the platform 22 slide over the filling rings 25 into theshield. The latter remains in position in the tunnel. When thetunnel-driving machine has left the shield, the latter can be knockeddown and be re-used in the next zone of low stability.

The milling cutters 5 normally operate ahead of the cutting edge of theshield. When the rock conditions deteriorate to such a degree that aproper excavation by the milling cutters disposed ahead of the cuttingedge of the shield can no longer be carried out, the hydraulic supplycan be changed for a short time from the jacks 18 to the propellingjacks 14 of the tunnel-driving machine so that the latter is retractedinto the shield. This is indicated with solid lines in FIG. 18. Duringthis operation, the tunneldriving machine and particularly itspropelling unit remains secured in the shield. Before the machine isretracted, the milling cutters must be adjusted radially inwardly sothat they will not collide with the annular cutting edge of the shield.When the tunnel-driving machine has been retracted, the hydraulic sourceis connected to the propelling jacks 18 and the shield tunneling withinstallation of the lining ring segments 20 is continued as described.When underground water is encountered or the tunnel is driven underrivers, straits or the like, compressed air may be used in the shield.The limiting working conditions will be reached when a proper excavationis not possible in spite of the increased air pressure in the tunnel andwith the tunnel-driving machine fully retracted.

To prevent a caving-in of substantial amounts of loose material, pockets26 which are open in front are secured to the drum 10 of thetunnel-driving machine 1 between the milling cutters 5. This isindicated in FIG. 19.

FIGS. 20 and 21 show two shield segments 9 and a bar 27 which iswedge-shaped in cross-section and inserted between those edge faces ofthe segments 9 which are parallel to the axis of the shield. Such bars27 enable an adaptation of the shield to different tunnel diameterswithout change of the segments 9. It is apparent from FIG. 22 that theuse of a relatively thick bar 27a results in a considerable increase ofthe diameter of the section formed by the segments 9. A stiffening rib28 is parallel to the axis of the shield and enables the segments 9 tocarry and guide the heavy tunnel-driving machine.

The stiffening ribs 28 enable also an assembling and disassembling ofthe shield segments by means of a device which differs from theinstalling device 11 and is shown in FIG. 22 to comprise an arm 29,which is pivoted to a suitable part or frame and carries a gripper 30,which can be radially adjusted by a crank handle 31 and opened andclosed by a crank handle 32.

What is claimed is:

1. A process of driving tunnels in rock having zones which differ instability, which comprises the steps of excavating zones of stable rockonly by a tunnel-driving machine having rotatable and radiallyadjustable cutting tools, advancing the tunnel-driving machine in stepsin a zone of stable rock to the transition to a zone of rock of lowcohesion and operating the tunnel-driving machine during such steps toexcavate on a diameter which is larger than the diameter of theexcavation in the preceding portion of the zone of stable rock,

retracting the tunnel-driving machine after each of said advancing stepswith the cutting tools is a radially inwardly adjusted position,

installing a section of tubular shield ahead of the tunnel-drivingmachine after each of said retracting steps and before the nextsucceeding advancing step, said section consisting of a plurality ofseparable segments,

anchoring the tunnel-driving machine in the shield,

advancing the shield through the zone of rock of low cohesion untilstable rock is reached,

lining the tunnel behind the shield with lining rings,

releasing the tunnel-driving machine from the shield when the stablerock is reached,

using the tunnel-driving machine alone for excavating the stable rock,and

knocking down the shield.

2. A process as set forth in claim 1, in which a tunneldriving machineis used in which said cutting tools consist of milling cutters adaptedto revolve in unison about the longitudinal axis of the machine.

3. A process as set forth in claim 1, in which the cutting tools of thetunnel-driving machine are operated to excavate during the advance ofthe shield.

4. A process as set forth in claim 1, in which said tunnel-drivingmachine is used for excavation alone in the zone of stable rock untilthe zone of rock of low cohesion is reached,

the tunnel-driving machine is subsequently retracted for a distancewhich is at least as large as the length of the tubular shield, and

the tunnel-driving machine is operated during said advancing steps toincrease the diameter of the previously excavated tunnel by twice thethickness of the shield segments.

5. A process as set forth in claim 4, in which an annular groove isexcavated in the tunnel wall ahead of the retracted tunnel-drivingmachine, and

the cutting tools of the tunnel-driving machine are adjusted in saidgroove to the increased diameter of excavation.

6. A process as set forth in claim 1, which comprises knocking down thetwo rearmost sections of the shield when the tunnel-driving machine hasadvanced ahead of said two rearmost sections,

replacing said two rearmost sections by sheet metal elements which areinstalled and welded together in situ to form a shield tail,

installing a thrust-bearing ring in said shield tail,

causing hydraulic jacks for advancing the shield to bear on saidthrust-bearing ring, and

installing the first lining ring behind the thrust-bearing ring.

7. Apparatus for driving tunnels in rock having zones which differ instability, said apparatus comprising a tunnel-driving machine having ahydraulically operable propelling unit,

a shield consisting of separable arcuate segments mounted about saidtunnel-driving machine and releasably connected to it,

a thrust-bearing ring,

hydraulic jacking means bearing on said thrust-bearing ring and operableto advance said shield, and

means for supplying hydraulic pressure fluid alternatively to saidpropelling unit and to said jacking means.

8. Apparatus as set forth in claim 7, said last-named means being a pumpfor supplying hydraulic pressure fluid alternatively to said propellingunit and to said jacking means.

9. Apparatus for driving tunnels in rock having zones which differ instability, said apparatus comprising a tunnel-driving machine comprisinga drum which is rotatable on the axis of said machine,

rotatable and radially adjustable cutting tools mounted on the leadingend face of said drum,

said apparatus further comprising a shield consisting of separablearcuate segments mounted about said tunnel-driving machine andreleasably connected to it,

means for alternatively advancing said tunnel-driving machine alone andsaid shield with said tunnel-driving machine and a bracketlikeinstalling device which is mounted at the leading end of the drum andcomprises handling means for handling said arcuate segments,

said handling means extending radially with respect to the axis of thedrum.

10. Apparatus as set forth in claim 9, in which said handling meanscomprise spindles extending radially with respect to the axis of thedrum.

11. Apparatus for driving tunnels in rock having zones which differ instability, said apparatus comprising a tunnel-driving machine comprisinga drum which is rotatable on the axis of said machine,

rotatable and radially adjustable cutting tools mounted on the leadingend face of said drum, and

forwardly open pockets provided on said leading end face of said drumbetween said cutting tools,

said apparatus further comprising a tubular shield consisting ofseparable arcuate segments mounted about said tunnel-driving machine andreleasably connected to it, and

means for alternatively advancing said tunnel-driving machine along andsaid shield with said tunnel-driving machine.

References (Cited UNITED STATES PATENTS 2,425,169 8/ 1947 Wilson 6l852,466,709 4/ 1949 Karr 61-85 3,061,287 10/1962 Robbins 29931 3,411,82611/1968 Wallers et al. 29931 FOREIGN PATENTS 114,413 1918 Great Britain.

ERNEST R. PURSER, Primary Examiner US. Cl. X.R. 299ll, 31, 33

